There is a growing interest in the toy industry for fibers which are useful in toys and which exhibit varying abilities to undergo color change. This interest is especially present in the area of children's dolls.
U.S. Pat. No. 3,382,607 discloses a toy having a visible portion comprising fibers permanently impregnated with an indicator dye capable of repeated and reversible color change in response to contact with liquids of different pH concentrations.
In U.S. Pat. No. 4,781,647, artificial doll hair is disclosed which is extruded from polymeric materials which is at least partially translucent, and which contains phosphorescent particles. The presence of the particles give unique color to the hairs without weakening the fiber. The polymeric material for the fiber can be a polyamide, polyester, polyolefin, polyacylonitrile, or polyvinyl chloride, coupled to the particles by silane or titanate coupling agent. In U.S. Pat. No. 4,276,207, pigment sensitized particles (PSP) are described as being completely encapsulated by the glycolate modified derivative. It is stated that the PSP particles will not stain the fiber regardless of composition and will wash out completely and easily with hot water, or mild soaping, hot or cold. It is further stated that the hair coloring of dolls was not possible with prior art dyestuffs since they would stain the doll's hair no matter what fiber was used--polypropylene, nylon, polyester, etc.
In other known processes, fibers are typically dyed using a thermal process.